fix: pin tailwindcss v3 in rag-ui and update npm lockfile

rag-playground uses @nuxt/ui v3 with tailwindcss v4, which pnpm
hoists to the workspace shared modules. rag-ui uses @nuxt/ui v2 which
depends on @nuxtjs/tailwindcss that requires tailwindcss v3 APIs.
Pinning tailwindcss ^3.4.0 as a direct devDep in rag-ui ensures pnpm
resolves v3 for that package instead of the hoisted v4.

Also updates rag-ui/package-lock.json (npm) to include vue-tsc and
the pinned tailwindcss, fixing the Docker frontend build npm ci failure.

Made-with: Cursor

Author: albegosu

pnpm-lock.yaml

@@ -21,6 +21,7 @@
     "@nuxt/devtools": "latest",
     "@types/node": "^20.10.0",
     "nuxt": "^3.9.0",
+    "tailwindcss": "^3.4.0",
     "typescript": "^5.3.0",
     "vue-tsc": "^2.0.0"
   }